This is one of a series of notes taken during the 2015 meeting of the AAS Division on Dynamical Astronomy, 3-7 May, at CalTech. An index to this series (all the papers presented at the meeting) is here.
Jonathan Bird (Vanderbilt) (invited)
Abstract
[None]
Notes
- Are disk galaxies formed by nature or nurture?
- e.g. NGC 891
- Thick disk and thin disk (Gilmore & Reid 1983)
- Extragalactic thick disks are ubiquitous (Dalcanton & Bernstein 2002, Yoachim & Dalcanton 2006)
- Nature:
- Stellar kinematics dominated by those of gas from which stars formed
- Subsequent dynamics are second-order
- Planetary disk: core accretion; static
- $\alpha$ abundance is a tracer for stellar age
- plot: [$\alpha$/Fe] vs [Fe/H]
- Thick disk is old, $\alpha$-rich, kinematically hot
- Thin disk is young, (relatively to Fe) $\alpha$-poor, dynamically cold
- Smooth correlation between chemistry and kinematics
- APOGEE survey: velocity dispersion increases with stellar age
- power law
- $\rightarrow$ disk grows over time
- Nurture:
- Stellar kinematics dominated by dynamical interactions after birth
- Most stars born in dynamical cold gas (level playing field)
- Resonances play huge role; pebble accretion
- Scattering processes heat stellar velocity distributions
- Radial migration
- Sellwood & Binney 2002: can redistribute stars without globally heating the disk
- Can outwardly migrating stars create the thick disk?
- No: vertical action is conserved. (Tolfree et al. 2014)